Diamond films are useful in a wide variety of applications such as providing heat sinks for microelectronic devices and cutting surfaces for industrial tools.
One known method for growing diamond films is by chemical vapor transport (CVT). CVT reactions of carbon for the deposition of diamond were reported by B. V. Spitsyn et al, 52 J.Crystal Growth 219-226 (1981). Subsequently, Piekarczyk and coworkers performed detailed thermodynamic analyses of the carbon-hydrogen binary system and examined carbon-hydrogen CVT theoretically in terms of a four-stage transport model. See W. Piekarczyk et at, 106 J.Crystal Growth 279-93 (1990). These investigators analyzed the solid-gas phase equilibria existing for graphite and diamond over a defined regime of pressure (0.1-10.sup.-8 atm.) and temperature (850-3000K.) in a closed system of hydrogen. From the solubility plots for graphite and diamond in hydrogen versus temperature, they constructed a model for the transport cycle leading to diamond deposition. Using the model, Piekarczyk and coworkers evaluated data reported in the literature and confirmed experimentally that deposition of diamond could proceed readily from gas solutions undersaturated with respect to diamond.
The difficulty with these known processes, however, is that along with diamond, they also deposit substantial amounts of graphite. High temperatures (1350-1650 C.) were used to rapidly react the carbon source (graphite) with hydrogen for deposition of diamond on a substrate at 600-1100C. In such cases the gas phase is saturated with graphite at even higher levels than for diamond. Thus, the certain deposition of graphite with respect to diamond occurs according to the reverse of the reaction EQU xC (.sub.s,gra)+1/2yH.sub.2(g) =C.sub.x H.sub.y(g)
The result, indicated by Raman spectra, is low quality film including high levels of graphite. Accordingly, there is a need for an improved process for depositing thin films of high purity diamond.